Direct injection gasoline engines may provide increased performance so that engine efficiency may be improved. Directly injecting fuel into a cylinder can reduce temperature in a cylinder so that more air and fuel may be drawn into the cylinder. However, the air-fuel mixture within the cylinder may not be fully vaporized at the time of ignition at higher engine speeds and loads since there is less time to mix air with the fuel. Consequently, a portion of injected fuel may not completely oxidize, thereby forming carbonaceous soot within the cylinder. After the soot is expelled from the engine, the soot may be stored in a particulate filter for subsequent oxidation; however, it may be challenging to initiate combustion in the particulate filter. One possible way to initiate regeneration (e.g., reduce an amount of soot stored in the particulate filter) in the particulate filter is to retard engine spark timing to increase cylinder exhaust port temperature. However, it may take longer than is desired for temperatures in the port to reach the particulate filter so that regeneration may begin.
The inventors herein have recognized the above-mentioned limitations and have developed an engine operating method, comprising: supplying a spark to combust an air-fuel mixture in an engine; storing particulate matter produced by combusting the air-fuel mixture in a particulate filter; and regenerating the particulate filter while engine load is less than a threshold and in response to a tip-out condition via ceasing to deliver spark to one or more cylinders and supplying fuel to the one or more cylinders.
By ceasing or stopping spark delivery to one or more cylinders, fuel can be supplied to the cylinder so that the fuel is ejected from the cylinders into the exhaust system where it may oxidize closer to the particulate filter. In one example, the fuel supplied to a cylinder where spark is inhibited may increase a temperature of a three-way catalyst positioned upstream of the particulate filter so that heat may be transferred from the three-way catalyst to the particulate filter. In this way, regeneration of a particulate filter may be initiated during low engine load conditions. For example, during vehicle deceleration after a tip-out (e.g., release of an accelerator pedal or a decrease in engine torque demand), spark supplied to a cylinder may be stopped while the engine continues to rotate via torque supplied by vehicle wheels. Fuel may be injected to cylinders where spark is stopped and then ejected to a three-way catalyst in an exhaust system shortly thereafter. The oxidizing fuel heats the particulate filter so that soot held within the particulate filter may be oxidized.
The present description may provide several advantages. Specifically, the approach may use fuel to regenerate a particulate filter in a more efficient manner. Additionally, the approach may provide improved emissions after particulate filter regeneration by improving catalyst chemistry. Further, the approach may provide increased opportunities for regenerating a particulate filter.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.